This invention relates generally to power conversion systems and, more particularly, to a method and apparatus for cooling power converters.
In the power generation industry, high speed generators are used to generate electrical power at relatively high frequencies (typically a number of times higher than the grid frequency), and power converters are used to convert the high frequency AC power down to an AC grid frequency of 50 or 60 Hz. This is accomplished by rectifying the high frequency AC signal and then generating a new sinusoidal AC wave of the desired frequency. The creation of the new wave involves the use of integrated gate bipolar transistors (IGBT's), which are switched at a carrier frequency rate, which is an order of magnitude higher than the power converter output frequency. Because of the necessary repeated on and off switching of the IGBT's, they generate a substantial amount of heat which must be dissipated. Without cooling this dissipated heat, the temperatures of solid state junctions in the IGBT's would exceed the maximum values, and the transformers would be permanently damaged. Accordingly, all high frequency power conversion equipment typically applies some type of cooling in order to control these junction temperatures.
The cooling requirement increases with power capacity in the IGBT's, and, at a given switching frequency, as the amount of current going through an IGBT is decreased, the heat that is developed will be decreased. Accordingly if the temperature of the solid state junction can be reduced, then the current being switched on and off through the junction can be increased to thereby enhance the power density of the power converter. Further, acceptable IGBT lifetime can be assured if the temperature of the solid state junction is kept below a certain maximum value.
Progress has been made in IGBT design to enable forced-convection air-cooled finned cold plates in removing the heat from the transistors. However, forced-convection air-cooling of finned cold plates is relatively ineffective due to the poor heat transfer between the cooling air and the finned cold plate.
It is therefore an object of the present invention to provide an improved cooling method and apparatus for a power converter.
Another object of the present invention is the provision in a power converter for more effectively cooling the transistors therein.
Another object of the present invention is the provision in a power converter for reducing the temperature of the solid state junctions while increasing the current flow therein.
Yet another object of the present invention is to improve the life of transistors in power conversion systems.
Still another object of the present invention is the provision for a power conversion system that is economical to manufacture and effective and efficient in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.